Dear,
Association of stiff person syndrome, is a rare disorder characterized by muscle rigidity, spasms and continuous motor unit activity. Its association with myasthenia gravis is rare but has been documented. Both, have similar pathogenesis and disease process linked to immunogenic abnormality. It may manifest as chronic pain and stiffness in the low back and both lower limbs.
Myasthenia gravis may precede stiff person syndrome, a rare association, not serendipitous, with diabetes mellitus and inflammatory thyroid disease.
intravenous immunoglobulin is the therapy.
All the best.